Pistons



A. CORNET July 1, 1 969 PISTONS Sheet or2 Filed Dec. 13, 1966 July 1, 1969 A, CORNET 3,452,649

PISTONS Filed Dec. 13, 1966 Sheet 2 of 2 FIG.4 F|G.5

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JM-FH United States Patent 3,452,649 PISTONS Andre Cornet, 31 bis Rue Louise Michel, 92 Levallois-Perret, France Filed Dec. 13, 1966, Ser. No. 601,483

Int. Cl. F16j 1/00 US. Cl. 92-232 13 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to improvements in the construction of pistons of all types, for heat engines, compressors and other machines, but concerns more particularly cast light alloy pistons for high temperature working.

Various improvements have been proposed in the construction of pistons with a view to reconciling the different and often contradictory needs of such pistons namely stability, lightness, rigidity, robustness, flexibility, gas tightness and good heat transmission. The applicant has already described in French Patents No. 1,176,476 of June 4, 1957, No. 1,187,277 of Nov. 26, 1957 and No. 1,209,789 of Sept. 13, 1958, pistons which, from this point of view, have numerous advantages over pistons then in use, which advantages have been subsequently confirmed by the results obtained in practice.

However, speeds of rotation, compression loads and other volumetric variations never cease to increase. These different requirements always accentuate the contradictory character of the different properties required by pistons, and this has led the applicant to effect many changes to the form of construction described in the aforesaid patents.

There will first be briefly recalled certain disadvantages to which known monobloc pistons are prone.

In such a piston, working clearances must be preserved between rubbing parts, this being particularly important for material such as aluminium having a high coefiicient of expansion. In order to reduce this clearance whilst still allowing free sliding of the piston at all speeds and temperatures without too much noise or slap, certain means must be employed such as machining the peripheral surface of this skirt according to an approximate ellipse, or the incorporation in the piston, during casting, of steel rings or plates to compensate for expansioneffects and to reduce deformations of the skirt.

Moreover, to correct expansion distortion, the skirt is often given an ogive profile in axial section, with a very pronounced increase in play at the ring-carrying portion of the piston head. This, however, results in unsatisfactory sealing and heat transmission and in a tendency for the piston to rock, as Well as in rapid wear of the piston rings, these various disadvantages reacting one with the other in such a way as to worsen their results.

It will also be recalled that in transverse section, in a monobloc piston, the two zones of the skirt situated at the minor axis of the ellipse are of considerable mass, forming bearing bosses for the gudgeon pin, whilst the skirt zones at the ends of the major axis of the ellipse are much thinner, and it thus follows that there will be critical points at the junctions of the thick and thin portions.

Again, with such an ellipse, contact between skirt and cylinder is only assured in a plane perpendicular to the pivotal axis of the gudgeon pin, insofar as such contact is compatible with the ogive form of the skirt when viewed in a section in this plane.

An object of the present invention is to provide a piston constructed in such a manner that the aforesaid difiiculties of manufacture as well as others, are minimized or avoided.

According to the present invention, a piston comprises a head portion having a piston head and an annular part grooved for the reception of sealing rings, a skirt, a plurality of bosses forming gudgeon pin bearings, and internal webs disposed to either side of the diametric plane of the piston normal to the axis of the bearings, said webs connecting said bosses to said skirt and head portion, and at least a portion of said webs converging towards the power thrust side of the piston.

The webs may be secured to the interior faces of both said piston head and said annular part of said head portion. The bearing bosses are thus connected to the piston head and this provides a direct passage for heat from the head to the skirt and from there to the cylinder, without creating a rigid mechanical connection between the head and skirt in the direction of transverse expansion. The webs also contribute to the transmission of motive force to the gudgeon pin.

The two extremities respectively of said webs connected to the skirt at the compression thrust side thereof are preferably provided with wide cut-away portions which are arranged so that said webs are separated from desired zones of said skirt adjacent to said piston head.

These zones are the ones most exposed to thermal ef fects and the aforesaid separation increases the flexibility of the zones.

The two gudgeon pins bearing bosses may be connected moreover to the piston head portion by complementary connection elements, said elements being free from all contact with said skirt. These elements improve the robustness of the assembly without introducing an unnecessary mechanical connection between the head portion and skirt. These complementary connection elements can comprise, for each bearing, two ribs disposed substantially along the axial direction of the bearing and being connected to that face of the boss nearest to the head portion as well as to the outer face of the respective web. The two ribs can be mutually connected at their outer edges by a prolongation of the annular part of the head portion, serving as an outer end plate of the bearing and disposed in a corresponding cut-away portion provided in the skirt.

A piston arranged in the manner described and provided with connection elements thus distributed possesses surprising advantages over known pistons both as regards sealing and good heat transmission, and the often contradictory qualities of robustness, rigidity, flexibility and stability. As will be seen from the following description with reference to the accompanying drawings, these advantages are attributable partly to the fact that the manner of construction of the piston of the invention, in which are clearly distinguished the zones subjected to heavy mechanical stress and those which, being at first sight similar, are only subject to moderate stress, the said manner taking this effect into account in distributing the robustness and flexibility unequally but as required by each zone. In the accompanying drawings:

FIGURE 1 is a sectional view of a piston of the invention taken along the diametric plane normal to the axis of the gudgeon pin;

FIGURE 2 is a sectional view along the line II-II of FIGURE 1;

FIGURE 3 is a sectional view along the line III-III of FIGURE 1;

FIGURE 4 is a section of the piston along the diametric plane normal to the gudgeon pin axis of another embodiment of piston;

FIGURE 5 is an elevation along the line VV of FIGURE 4;

FIGURE 6 is an elevation along the line VI-VI of FIGURE 5;

FIGURE 7 is a section along the line VIIVII of FIGURE 6;

FIGURE 8 is an end view along the line VIII-VIII of FIGURE 6;

FIGURE 9 is a section along the line IX-IX of FIG- URE 7.

There is shown diagrammatically in FIGURE 1 a piston 1 disposed within a cylinder 2 and comprising a head portion 3, a skirt 4 and two bearings 5, both of which are visible in the sectional view of FIGURE 2. The elements 3, 4 and 5 are joined by connection elements to be described hereinafter, the assembly forming an integral unit formed by casting.

The head portion 3', comprises a piston head 6 and an annular portion 7 in which are provided grooves for the reception of sealing rings and possibly a protecting ring of the kind described by the applicant in the Patent No. 1,388,665 dated July 4, 1963, the corner extremity of the portion 7 being shown at 7A.

Two thin internal webs 9 are connected respectively by their inner faces to the inner end faces 10 of the two bearings 5, and are also connected to the inner face of the skirt 4 and to the parts 6 and 7 of the head portion 3.

As shown in FIGURE 3, each of the two bearings 5 is connected to the inner face of the piston head 6 by means of two ribs 11 and 12 connected to a respective web 9 and stemming from the face of the bearing nearest to the piston head 6. The ribs 11 and 12 are mutually connected at their outer edges by an element 13 formed partly by a sector of the annular part 7 and partly by a prolongation of this sector, the prolongation being connected to the outer end face of a respective one of the bearings 5.

Moreover, it will be seen in FIGURES 1 and 3 that each of the webs 9 has a recess 14 in the space defined by the two ribs 11 and 12, the interior face of the piston head 6 and the face of the bearing disposed nearest to the piston head 6.

FIGURE 2 shows that the skirt 4 has a cut-away portion 15 in the vicinity of each bearing 5 and is thus divided, over part of its height, into two sectors 16 and 17. It will be seen moreover in FIGURE 2 that the two webs 9, disposed obliquely with respect to each other, rejoin the skirt sector 16 in the vicinity of the same generatrix 18, whilst they join the opposite sector 17 at two generatrices 19 and 20.

The sector 17 has a compensation slot 21 extending along its whole height, and, as seen in FIGURE 1, the edge 7A of the ring-carrying annular part 7 opposite to the skirt is separated from all direct contact with the Webs 9, which have to this end deep grooves extending from the side of the sector 17 into large cut-away portions 22.

The head portion 3 and the skirt 4 are machined so that their outer faces are truly cylindrical and defined by true circles, the diameter of the head portion being usually less than that of the skirt.

The arrangement thus provided exhibits the following advantages:

It allows the ring-carrying head portion to expand independently of the skirt because the only connection between these two elements is constituted by the two webs 9;

Each web 9, interrupted by a cavity 14 and connected to the elements 11, 12 and 13, forms, with the latter, a thin arched portion constituting a flexible assembly allowing the annular part 7, which is simply machined on a lathe, to retain its circular cylindrical form under expansion effects;

The webs 9, although thin, provide a direct heat path from the head to the skirt and to the cylinder walls and contribute to the transmission to the bearings 5 of the motive force exerted on the head 3;

The elements 11, 12 and 13, although sufficiently deformable in the transverse direction to allow free expansion of the head portion 3, constitute in the axial direction of the piston an extremely rigid connection between the head portion 3 and the bearings 5;

The webs 9, disposed obliquely with respect to each other, provide the skirt 4 with an extremely stable three point support;

The convergence of the webs 9 on the skirt sector 16 allows free expansion of the latter by reason of common contact generatrix of the two webs, whilst providing it with a firm support; the sector 16 is thus particularly well adapted to form the power thrust side of the piston;

The relative weakness of the skirt sector 17, resulting from the spacing of the webs 9 at that side, imparts to this sector the flexibility desired in view of the tendency of the piston to rock;

The free expansion of this sector is aided by cut-out portions 22 provided in the webs 9 and by the compensation slot 21;

The assembly, resulting from the oblique disposition of the webs 9 and of the presence of the cut-away portions 22 and the slot 21, also allows the skirt to main- Lain its circular cylindrical form under the effects of cat.

FIGURES 4 and 9 show more clearly another embodiment of the piston described above. A detailed description of these figures will not be given since they contain elements analogous with those of FIGURES 1 to 3 which are represented by the same reference numerals as in the latter figures.

It.is simply pointed out that in FIGURE 9 the webs 9 only converge towards the skirt section 16 by their portions 9a adjacent to this sector whilst their portions 9b disposed opposite sector 17 are parallel with each other. The curvature of portion 9a has a favourable effect on the free expansion of the skirt under the effects of heat.

It will be seen moreover, in FIGURE 6, that cut-away portions 15 are provided in the skirt 4 in the vicinity of each bearing 5. Further large cut-away portions 22 are provided at the base of the skirt below each bearing 5 and portion 15. The narrow bands 23, remaining between the cut-away portions 15 and 22, form, in practice, flex- 1ble joints between the sectors 16 and 17 of the skirt which again facilitate thermal deformations. As shown 1n FIGURES 4 and 7, the pockets 14 provided in the webs 9 may contain a complementary rib 12a, parallel to the ribs 11 and 12.

A series of comparative trials was organized on different engines equipped on the one hand with their normal pistons and on the other with pistons of the present invention made according to FIGURES 4 to 9. So as not to detract from the accuracy of the comparisons, the pistons of the invention were made from the same alloy as the known reference pistons and their dimenslons were chosen so as to produce pistons of substantially equal weight.

Such trials were carried out on two air-cooled engines; 2 CV Citroen, Panhard, and two water-cooled engines; Peugeot 403, Simca Flash.

There will now be given by way of example some results of a cycle of test bed trials of 20 hours duration on two 2 CV Citroen engines of 425 cubic centimetres, one (No. being eq ipp d with its origi a P the other (No. 2) with a set of pistons according to the invention.

Over an increasing range of revolutions starting from 1500 revs./min., there were measured the couple C (in kilogram metres), the power P (in HP) and the specific consumption SC (in grams/HP/h.). Up to 4000 revs./ min., substantially equal performances for the two engines were measured, namely:

Revs/min. C P SO Beyond 4000 revs/min. however:

Engine No. 1 exhibited a fall in power, whilst engme No. 2 ran easily up to 4400 revs/min. where it was observed that:

C=2.18 kilogram metres P: 13.20 HP SC=310 grams/HP/h.

The fall-off in power only appeared beyond 4400 revs./ min.

Moreover, engine No. 2 gave off less exhaust smoke and gave slightly less oil consumption.

After the 20 hours test cycle, the pistons were dismantled and checked. On the known (engine No. 1) it was seen that the contact surfaces of the skirt were badly distributed: pin-point bearing zones could only be seen distributed along two generatrices disposed to one side of the axis of oscillation. On the pistons of engine No. 2, contact appeared to have occurred over the Whole periphery of the skirt.

There were also carried out static tests to compare the resistance to breakage of the pistons.

These tests were caried out on an Amsler machine, the 1 drive being exerted between the piston head and the gudgeon pin. In the case of two pistons (for a Panhard engine) of 75 mm. diameter, the breakage occurred at 3.5 tons for the known piston at 11.3 tons for the piston according to the invention.

These various trials confirm that the better guiding capability, the absence of rocking effects, and the good thermal conduction of the piston of the invention assure better sealing when hot and improve the performances of engines equipped therewith. The results of static trials, which revealed surprising increases in the safety margin, open new horizons in the field of piston manufacture, making it possible to envisage the production of pistons by die-casting. This more rapid process of manufacture is not possible at present because metal obtained by diecasting has mechanical charatceristics less favourable than in chill casting.

It will be understood that the invention is not limited to the embodiments described and shown but includes all variations and detail modifications.

Thus, for example, by increasing the angle 19-18-20 (FIGURE 2), one can dispense wtih slot 21 and the large separation 22 of the partitions 9: the flexibility required from sector 17 of the skirt then results from simple spacing of the connections of the webs 9.

What I claim is:

1. A piston comprising a head portion having a piston head and an annular part grooved for the reception of sealing rings, a skirt, said skirt comprising opposite sectors joined by annular band portions, two bosses forming gudgeon pin bearings and having respective integral webs connected to said head portion and to said skirt and disposed on each side of the diametric plane of the piston normal to the axis of the bearings, said webs having portions converging towards and in approximate contact with each other at the power thrust side of the skirt and further oppositely extending portions connected to the compression thrust side at two points of the skirt encompassing a relatively wide region therebetween.

2. A piston according to claim 1, wherein said further oppositely extending web portions are mutually parallel.

3. A piston according to claim 1, wherein said skirt is spaced from said head portion and from said bosses.

4. A piston according to claim 1, wherein the outer face of said skirt is a true cylindrical face defined by a true circle.

5. A piston according to claim 1 having a compensation slot in the side of the skirt opposite said power thrust side.

6. A piston according to claim 1 wherein said webs are secured to the interior faces of both said piston head and said annular part of said head portion.

7. A. piston according to claim 1 wherein wide cutaway portions are formed in the said further portions of said webs and arranged so that said webs are separated from desired zones of said skirt adjacent to said piston head.

8. A piston according to claim 1 comprising complementary connection elements between said bosses and said head portion, said elements being free from all contact with said skirt.

9. A piston according to claim 8 wherein two said elements are provided for each said boss, said elements being ribs disposed substantially along the axial direction of said boss, and being connected to that face of said boss opposite to said head portion as well as to the outer faces of the respective Web means.

10. A piston according to claim 9 wherein each of said webs has an opening extending between said ribs over the depth of said head portion.

11. A piston according to claim 9 wherein the outer face of said skirt and the outer face of said annular part are true cylindrical faces defined by true circles.

12. A piston according to claim 9 wherein each pair of ribs is connected at the outer edges of said ribs by a. prolongation of said annular part, said prolongations serving respectively as an outer end plate of each of said bearings, corresponding cut-away portions, being formed in the skirt to accommodate said prolongations.

13. A piston according to claim 1 wherein at least a portion of each web has a curved profile when viewed in section following a plane normal to the axis of the piston.

References Cited UNITED STATES PATENTS 1,499,073 6/1924' Pomeroy 92-235 X 1,763,523 6/1930 Iardine 92236 1,944,223 1/1934 Day 92232 2,066,613 1/1937 Day 92 -235 2,147,819 2/1939' 1 Long 92225 2,398,005 4/1946 Howlett 92-236 3,009,749 11/1961 Cornet 92236 CARROLL B. DORITY, JR., Primary Examiner.

US. Cl. X.R. 92-236 

